Metallicities and abundance ratios from quasar broad emission lines

Fred Hamann, K. T. Korista, G. J. Ferland, Craig Warner, Jack Baldwin

Research output: Contribution to journalArticlepeer-review

147 Scopus citations

Abstract

The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs) are important diagnostics of the relative abundances and overall metallicity in the gas. Here we present new theoretical predictions for several UV BELs. We focus specifically on the relative nitrogen abundance as a metallicity indicator, based on the expected secondary enrichment of nitrogen at metallicities Z ≳ 0.2 Z. Among the lines we consider, N III] λ1750/O III] λ1664, N V λ1240/(C IV λ1549 + O VI λ1034), and N V/He II λ1640 are the most robust diagnostics. We argue, in particular, that the average N v BEL is not dominated by scattered Lyα photons from a broad absorption-line wind. We then compare our calculated line ratios with observations from the literature. The results support earlier claims that the gas-phase metallicities near quasars are typically near or several times above the solar value. We conclude that quasar activity is preceded by, or coeval with, an episode of rapid and extensive star formation in the surrounding galactic (or protogalactic) nuclei. Chemical evolution models of these environments suggest that, to reach Z ≳ Z in well-mixed interstellar gas, the star formation must have begun ≳ 108 yr before the observed quasar activity.

Original languageEnglish
Pages (from-to)592-603
Number of pages12
JournalAstrophysical Journal
Volume564
Issue number2 I
DOIs
StatePublished - Jan 10 2002

Keywords

  • Galaxies: abundances
  • Galaxies: formation
  • Galaxies: nuclei
  • Line: formation
  • Quasars: emission lines
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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